1. Field of the Invention
The present invention relates to an electrode and a method of fabricating the same, and more particularly, to a low impedance gold electrode and a method of fabricating the same.
2. Description of the Related Art
An electrical and electronic device, such as a semiconductor device or a micro electro mechanical system (MEMS), has a plurality of electrodes. In general, gold (Au) electrodes are used in those devices as they have improved stability and reduced resistance or impedance.
An electrode, such as an electrode of a biosensor, is generally soaked in an electrolyte solution, and thus a gold electrode is often used in the biosensor in order to improve stability and reduce impedance of the electrolyte solution. However, even though the gold electrode is soaked in the electrolyte solution, an electrical double layer tends to form at an interface between the gold electrode and the electrolyte solution. That double layer impedes the flow of current through the electrolyte solution, thereby resulting in a very high impedance that can be, for example, on the order of tens of kilo-ohms (kΩ) or so.
In general, as the impedance of an electrode decreases, the biosensor is robust with respect to noise. When the electrode is soaked in the electrolyte solution, however, as the surface area of the electrode increases, the number of electrons passing through the electrical double layer increases. Accordingly, the surface area and the impedance of the electrode soaked in the electrolyte solution are inversely related to each other.
There are two methods of increasing the surface area of an electrode, especially, a gold electrode.
The first method is platinum (Pt) plating. The platinum plating involves immersing a gold electrode in a platinum plating solution to coat a surface of the gold electrode with platinum. Thus, the platinum plating increases the surface area of the gold electrode and thus the impedance of the gold electrode is reduced. However, the platinum plating has problems in that the gold electrode coated with platinum is easily damaged due to a weak bonding force and platinum is expensive.
The second method is gold electrode etching in which a surface of a gold electrode is etched with sulfuric acid. The gold electrode etching involves immersing a gold electrode in a sulfuric acid solution and removing a part of the gold electrode. However, the gold electrode etching has problems in that an increased surface area to an original surface ratio is small due to the low reactivity of gold so that the resultant impedance change ratio is also small. For example, it is difficult to even achieve a reduction in the impedance of the gold electrode by half via gold electrode etching. Accordingly, the platinum plating method is generally preferred over the gold electrode etching.
While gold electrodes are often used for electrical and electronic devices, such as semiconductor devices and MEMSs, as described above, the gold electrodes often suffer an additional drawback arising from poor contact problems due to a weak bonding force with other materials.